500 AMERICAN JOURNAL OF OPHTHALMOLOGY April, 1986

has a limited role in the management of intra­ocular foreign bodies, the retention rate offoreign bodies after pars plana vitrectomy inskilled hands is almost nil. Therefore, secon­dary complications from siderosis or chalcosisare greatly reduced if not totally eliminated.The potential risks of vitrectomy are morefairly viewed in this context.

THOMAS R. FRIBERG, M.D.Pittsburgh, Pennsylvania

Reference

1. Rosenthal, A. R., Marmor, M. F., Leuenberger,P., and Hopkins, J. L.: Chalcosis. A study of naturalhistory. Ophthalmology 86:1956, 1979.

_______ Reply _

EDITOR:A major point of our article was to reem­

phasize the value of the magnet as a first-lineapproach for removal of magnetic intraocularforeign bodies. We believe that, as the popu­larity of microvitreous techniques has in­creased, there has been a definite trend todeemphasize the importance of the magnetwhich is, comparatively speaking, simpler,less invasive, and can produce excellent long­term visual results. We are pleased that Dr.Friberg agrees that magnet extraction still hasa role in foreign body management. We donot intend to detract from the importance ofpars plana vitreous microsurgical techniqueswhere the magnet fails or is not indicated.

The criticism of our allowing retention of abrass foreign body in our Patient 11 is welltaken, and we respect Dr. Friberg's opinionregarding the risk of long-term complicationsin observing this patient. We also agree that a31% retention rate, with our Patients 3, 7, and10 also having retained foreign bodies, is un­desirable. However, initial visualization of theforeign body in these patients was suboptimalbecause of vitreous hemorrhage, and forcepsremoval would have required posterior vitrec­tomy for adequate exposure. The advisabilityof immediate posterior vitrectomy is question­able at best because of increased complica­tions such as intraoperative hemorrhage fromearly posttraumatic vascular engorgement andcontusion. 1 This leaves one with the option of

observation with intervention when complica­tions develop or undertaking foreign body ex­traction electively after inflammation has sub­sided but with the foreign body encapsulatedby fibrous tissue, making the surgical extrac­tion hazardous." In our opinion the choice be­tween these two hazards is not clear-cut inmany cases.

The risk of a potentially dangerous surgicalintervention must be carefully weighedagainst the risks of ocular toxicity of the re­tained foreign body.

JOHN P. SHOCK, M.D.DONALD F. ADAMS, M.D.

Little Rock, Arkansas

References

1. Gregor, F., and Ryan, S. J.: Combined posteriorcontusion and penetrating injury in the pig eye. IIi.A controlled treatment trial of vitrectomy. Br. J.Ophthalmol. 67:282, 1983.

2. Slusher, M. M., Sarin, L. K., and Federman,J. L.: Management of intra retinal foreign bodies.Ophthalmology 89:369, 1983.

Pigmentary Glaucoma Associated WithPosterior Chamber Intraocular Lenses

EDITOR:I read with interest the article, "Pigmentary

glaucoma associated with posterior chamberintraocular lenses" (Am. J. Ophthalmol.100:385, Sept. 1985) by J. R. Samples andE. M. Van Buskirk. I have recently seen andtreated two patients with the identical syn­drome. Both of my patients were diabetic andI presumed their problem to be related to"lacy vacuolization" of the iris pigment epi­thelium commonly associated with diabetesmellitus."

Although no mention was made in this arti­cle of the patients' underlying medical prob­lems, this information is important because itwould clarify whether this new syndrome iswidespread or confined to the diabetic popu­lation.

ROBERT C. CYKIERT, M.D.New York, New York

Vol. 101, No. 4 Correspondence 501

Reference

1. Hogan, M. J., and Zimmerman, L. E.: Ophthal­mic Pathology, 2nd ed. Philadelphia, W. B.Saunders. 1962, p. 408.

_______ Reply _

EDITOR:We are reluctant to generalize about the co­

incident occurrence of two common abnormal­ities when we have only observed a smallnumber of patients.

In one of our patients diabetes was con­trolled by diet alone, but the other five pa­tients demonstrated no clinical evidence of di­abetes mellitus. Hence, the syndrome is notconfined to eyes with diabetic iris abnormali­ties. Despite our awareness of abnormalitiesin the diabetic iris, we do not know of suffi­cient data to demonstrate whether or notcomplications of posterior iris chafing fromintraocular lens implants is more frequentamong patients with diabetes. We too haveobserved a remarkably high incidence of dia­betes in subsets of patients (in our case, ofposterior chamber lens-pupillary block), butwe are reluctant to generalize about a causa­tive relationship from examination of a smallnumber of patients. We are grateful to Dr.Cykiert for his interest in our patients andwill watch closely for the development of pig­ment dispersion in our diabetic patients withintraocular lens.

]OHNR. SAMPLES, M.D.E. MICHAEL VAN BUSKIRK, M.D.

Portland, Oregon

The Effects of Hypotonic andHypertonic Solutions on the Fluid

Content of Hydrophilic Contact Lenses

EDITOR:The recent interest in the in vivo dehydra­

tion of hydrogel contact lenses has led to thedevelopment of the term "percent dehydra­tion." Unfortunately, this term does notclearly specify under what equation dehydra­tion has been calculated, and so data from

studies of dehydration are easily misinterpret­ed. Firstly, consider the example of a 75%water content lens that weighs 50 mg. It iscomposed of 12.5 mg of polymer and 37.5 mgof water. A typical amount of dehydrationduring wear would be a loss of around 10 mgof water. There is, therefore, 27.5 mg of waterin the lens after dehydration, and a newwater content of 68.8% may be calculated.The percentage decrease in the total lensmass is 20%. The percentage decrease in thewater mass is 26.7%. The decrease in watercontent is 6.3%, which is a relative decreasein water content of 8.3%. Thus, the value ofthe "percentage dehydration" could be 20%,26.7%,6.3%, or 8.3% depending on the def­inition.

Secondly, it is of interest to note that alow-water-content lens may have a greaterrelative decrease in water content than ahigh-water-content lens, and yet have a con­siderably less percentage decrease in totallens mass. This occurs because proportionate­ly large changes in total lens mass accompanysmall changes in the water content for high­water-content lenses.

Thirdly, when considering the effects of de­hydration, it is important to ascribe a particu­lar clinical effect to the correct definition. Asan example, the change in water contentshould be used for calculations of the effect ofdehydration on oxygen transmissibility, butthe percentage decrease in total lens massmay be more appropriate for consideringchanges to the shape of a lens with dehydra­tion.

In their article, "The effects of hypotonicand hypertonic solutions on the fluid contentof hydrophilic contact lenses" (Am. J. Oph­thalmol. 99:521, May 1985), J. P. Aiello andM. S. Insler described the results by the term"percent of water loss." Aside from the con­fusion that this term creates, the failure tostate clearly the definition under which theresults were calculated renders comparison topreviously reported data of little value. Exam­ination of their methods leads to the beliefthat they calculated percentage loss of lensmass. However, they compared their percent­age figures directly with the results of Andra­sko;' who calculated the percentage decreasein water content, not lens mass. They inap­propriately reported Andrasko as findingequilibrium values at 80% to 93% of the fullysaturated water weight-this should read